Optical feedthrough assembly for use in implantable medical device

ABSTRACT

An optical feedthrough assembly is provided that is configured to be disposed through the canister of an implantable medical device. The optical feedthrough assembly comprises a ferrule having an aperture therethrough and an inner surface therethrough. An optical fiber passes through the aperture, and a compression seal stack is disposed within the aperture and around the optical fiber. The compression seal stack sealingly engages the optical fiber and the inner surface.

CROSS REFERENCE TO PRIORITY APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/380,248, filed Apr. 26, 2006, now allowed, which is hereinincorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates generally to implantable medical devices and,more particularly, to an optical feedthrough assembly for use in animplantable medical device.

BACKGROUND OF THE INVENTION

Implantable medical devices (IMDs) are now being equipped with biosensorsystems capable of monitoring optical characteristics (e.g., changes inrefractive index or reflectivity) indicative of physiological conditions(e.g., temperature, pressure, blood oxygen content, rate of chemicalprocessing, etc.). An IMD may now be equipped with, for example, afiber-linked optical interferometric system capable of monitoringhydrostatic pressure at a chosen site within a patient's body; e.g.,blood pressure within an artery. In such a system, the proximal end of aflexible, elongated catheter is coupled to an IMD and the distal end ofthe catheter is positioned adjacent the site to be optically monitored.The catheter carries an optical fiber, which is optically coupled to atransceiver disposed within the IMD's canister. The transceiver directsoutgoing light signals into the proximal end of the fiber, whichpropagate through the optical fiber until they reach the fiber's distalend. The light signals are then modulated by the body fluid (e.g.,blood) being monitored and are reflected back into the fiber. Themodulated signals propagate through the optical fiber once again and arereceived by the transceiver at the fiber's proximal end. The transceiveranalyzes characteristics (e.g., amplitude in an interferometer) of thereturning signals, and control circuitry coupled to the transceiverdetermines the blood pressure at the distal end of the catheter.

An optical feedthrough is utilized to guide the optical fiber throughthe canister of the IMD. The feedthrough may comprise a ferrule (e.g.,titanium) having an aperture therethrough through which the opticalfiber passes. To protect the circuitry of the IMD and to secure theoptical fiber within the ferrule, a hermetic seal is formed between aninner surface of the ferrule and an outer surface of the optic fiber.Traditionally, the hermetic seal has typically been formed by way of aco-firing or brazing process. For example, a window-ferrule braze may beformed by threading an annular ceramic or metal (e.g., gold) preformover the window and positioning the preform against an inner shelfprovided within the ferrule. If a matched seal is to be formed, thecomponents are chosen to have similar coefficients of thermal expansion,and an inner surface of the ferrule may be metalized prior to insertionof the preform. Next, the feedthrough assembly is heated in a furnace(e.g., to over 700 degrees Celsius for approximately 10-15 minutes) tocause the brazing compound to wet the glass and flow against the ferruleto form a seal. An annealing step is then performed, and the feedthroughassembly is allowed to cool to room temperature.

Glass-to-metal seals are relatively rigid and thus may crack if placedunder significant mechanical and thermal stress, which may promote thechemical degradation of the seal. Furthermore, conventional co-firing orbrazing processes utilized to produce glass-to-metal andceramic-to-metal seals subject the optical fiber, or window, to extremetemperatures and thus limit the materials from which the fiber may bemade, notably eliminating from consideration plastic optic fibers (POFs)made from flexible and low-cost polymers such as polymethylmethacrylate(PMMA), polystyrene, and polycarbonate. Additionally, co-firing andbrazing processes may be relatively complex, costly, and time consumingto perform.

In view of the above, it should be appreciated that it would bedesirable to provide an optical feedthrough assembly suitable for use inconjunction with optical fibers comprising a wide range of materials,including POFs. In addition, it would be advantageous if such an opticalfeedthrough assembly employed a polymeric compression seal thattolerates mechanical stress relatively well and that exhibits a highdegree of resistance to chemical degradation. It would be of furtherbenefit if such feedthrough assembly could be manufactured economicallyand efficiently. Furthermore, other desirable features andcharacteristics of the present invention will become apparent from thesubsequent detailed description of the invention and the appendedclaims, taken in conjunction with the accompanying drawings and thisbackground of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of theinvention and therefore do not limit the scope of the invention, but arepresented to assist in providing a proper understanding. The drawingsare not to scale (unless so stated) and are intended for use inconjunction with the explanations in the following detaileddescriptions. The present invention will hereinafter be described inconjunction with the appended drawings, wherein like reference numeralsdenote like elements, and:

FIGS. 1 and 2 are an isometric cross-sectional and side cross-sectionalviews, respectively, of an optical feedthrough assembly in accordancewith a first embodiment of the present invention;

FIG. 3 is an isometric view of the compression ring shown in FIGS. 1 and2;

FIG. 4 is a cross-sectional view of the optical feedthrough assemblyshown in FIGS. 1 and 2 after compression and crimping;

FIG. 5 is an isometric view of an apparatus suitable for compressing andcrimping the optical feedthrough assembly show in FIGS. 1, 2, and 4;

FIG. 6 is a more detailed isometric view of the lower jaw of theapparatus illustrated in FIG. 5;

FIG. 7 is a cross-sectional view of an implantable medical deviceemploying the optical feedthrough assembly shown in FIGS. 1, 2, and 4;

FIG. 8 is an isometric view of the implantable medical device shown inFIG. 7 implanted within a patient's body; and

FIG. 9 is an isometric cross-sectional view of an optical feedthroughassembly employing a truncated fiber or window in accordance with asecond embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The following description is exemplary in nature and is not intended tolimit the scope, applicability, or configuration of the invention in anyway. Rather, the following description provides a convenientillustration for implementing an exemplary embodiment of the invention.Various changes to the described embodiment may be made in the functionand arrangement of the elements described herein without departing fromthe scope of the invention.

FIGS. 1 and 2 are isometric cross-sectional and side cross-sectionalviews, respectively, of an optical feedthrough assembly 30 in accordancewith a first embodiment of the present invention. Feedthrough assembly30 comprises a ferrule 32 (e.g., titanium) having a first end region 34and a second end region 36. End region 34 includes an outer steppedportion 38 that may be fixedly coupled (e.g., welded) to the canister ofan implantable medical device as described more fully below inconjunction with FIG. 7. End region 34 also includes a retaining portion40, which may be, for example, a crimpable collar. A generallycylindrical cavity 42 extends through ferrule 32 from end region 34 toend region 36. An optical fiber 44 passes through cavity 42. Opticalfiber 44 may be a multi-mode or single mode fiber. The core of opticalfiber 44 comprises an optically transparent material through which lightsignals may be transmitted. The core of optical fiber 44 may comprise,for example, glass (e.g., silica), quartz, or any one of a variety ofpolymers, including polymethylmethacrylate (PMMA), polystyrene, andpolycarbonate. The core of optical fiber 44 may be sheathed in acladding (e.g., silica glass) having an index of refraction slightlyhigher than that of the fiber's core. Light signals introduced into theproximal end of the core of fiber 44 will successively internallyreflect off the cladding and thus propagate axially along the fiber'score until they reach the distal end of optical fiber 44. However, itshould be appreciated that many optical fibers (e.g., POFs) do notrequire an outer cladding to achieve total internal reflection,including optical fibers that are of a relatively short length, such asthose utilized as optical windows.

A polymeric compression seal stack 46 is disposed within ferrule 32 andguides optical fiber 44 through cavity 42. Compression seal stack 46 maycomprise a wide variety of components and configurations; however, inthe illustrated embodiment, compression seal stack 37 comprises threecomponents: (1) a compression ring 48, (2) a first compression ring seat50, and (3) a second compression ring seat 52. Compression ring 48 andring seats 50 and 52 each have a generally ring-shaped geometryincluding a central aperture therethrough for receiving fiber 44.Compression seal stack 46 is formed as ring seat 52, compression ring48, and ring seat 50 are each threaded over fiber or window 44 insuccession and inserted into ferrule 32 through end region 34.Compression seal stack 46 is prevented from exiting ferrule 32 throughend region 36 by an inner step 54, which abuts ring seat 52 as shown inFIGS. 1 and 2.

Compression ring 48 may assume a variety of forms; for example, as shownin FIG. 3, compression ring 48 may assume a generally torroidal formhaving a generally circular cross-section. Compression ring 48 ispreferably made of a compressible silicon-based material, although othercompressible materials may be utilized, including a flouroelastomerco-polymer of vinylidene fluoride and hexaflouropropylene, ethylenepropylene diene monomer rubber, polychloroprene, acrylonitrile butadieneco-polymer, and/or polysulphide. As ring 48 may be made of a polymericmaterial, compression ring 48 may tolerate mechanical stress and resistchemical degradation more effectively than prior art glass- orceramic-to-metal seals. In contrast to compression ring 48, compressionring seats 50 and 52 comprise a more rigid material. For example,compression rings seats 50 and 52 may be made from hard plastic, glass,porcelain, alumina, or chromium doped alumina. Alternatively, ring seats50 and 52 may be machined from a metal or alloy. If ring seats 50 and 52may come into contact with biological fluids, the material chosen forring seats 50 and 52 should obviously be biocompatible (e.g., abiocompatible metal, such as titanium, stainless steel, cobalt-chromiumalloys, or tantalum).

When force is applied to compression ring seat 50 in the direction ofcompression ring seat 52, compression ring 48 is compressed betweenseats 50 and 52. This causes compression ring 48 to radially expand andsealing engage an outer diameter of optical fiber 38 and an innersurface of ferrule 32. A hermetic seal is thus formed within ferrule 32.After compression seal stack 46 has been compressed in this manner,collar 40 may be subsequently crimped (i.e., deformed inward) to contactring seat 50 and thus secure compression seal stack 46 in its compressedstate. Compression and crimping of optical feedthrough assembly 30 maybe accomplished through the use of a compression and crimping tool, suchas that described below in conjunction with FIGS. 5 and 6.

FIG. 5 illustrates a compression and crimping apparatus 56 suitablecompressing seal stack 46 and crimping collar 40 of optical feedthroughassembly 30 (FIGS. 1, 2, and 4). Apparatus 56 comprises a firstcompression jaw 58 and a second compression jaw 60 (shown in greaterdetail in FIG. 6). Jaws 58 and 60 are coupled to a track (not shown) andmay move relative to one another in a clamp-like fashion. To facilitateproduction, compression jaws 58 and 60 may be incorporated into anautomated system. Typically, the compressing and crimping process isperformed after feedthrough assembly 30 is welded to the canister of animplantable medical device; however, feedthrough assembly 30 is shownindependently in FIGS. 5 and 6 for clarity.

Compression jaws 58 and 60 include respective openings 62 and 64 (e.g.,two slots) for receiving therein upper and lower segments of opticalfiber 38. Compression jaw 58 further includes a well portion 66 having agenerally inclined surface. An island 68 having an opening 70 thereinprotrudes upward from a central portion of well 66. The compression andcrimping process begins as optical feedthrough assembly 30 is loadedonto apparatus 56 and optical fiber 44 is received in openings 62, 64,and 66 as shown in FIG. 5. Next, jaws 58 and 60 are moved toward oneanother such that jaw 58 engages ferrule 32 proximate end portion 34 andjaw 60 engages ferrule 32 proximate end portion 36. Island 68 extendsinto cavity 42 proximate end portion 34 to contact compression ring seat50. This forces ring seat 50 towards ring seat 52 thus compressing ring48 between seats 50 and 52. As explained above, this results in theformation of a hermetic seal within ferrule 32. After seal stack 46(FIGS. 1, 2, and 4) has been compressed in this manner, well 66 engagesferrule 32 and crimps collar 40. That is, the included surface of well66 bears against collar 40 and causes collar 40 to deform inward overring seat 50. In this way, collar 40 secures compression seal stack 46in its compressed state and thus maintains the integrity of the hermeticseal within ferrule 32. Considering the forgoing paragraphs, it shouldbe appreciated that the above-described compression and crimping processmay be performed with less cost and more efficiently than conventionalco-firing or brazing processes that require the heating and cooling ofglass or ceramic preforms.

FIG. 7 is a functional view of a portion of an implantable medicaldevice (IMD) 80 incorporating optical feedthrough assembly 30 shown inFIGS. 1, 2 and 4. IMD 80 comprises a canister 82 (e.g., titanium,aluminum, stainless steel, etc.) that houses control circuitry 84, abattery 86, and a transceiver 88. Battery 86 is coupled to controlcircuitry 84 and to transceiver 88 as is shown at 90 and 92,respectively. In addition, control circuitry 84 is electrically coupledto transceiver 88 as is shown at 91. An aperture 94 is provided throughcanister 82 to accommodate feedthrough assembly 30. Assembly 30 isdisposed through aperture 94 and fixedly coupled (e.g., welded) tocanister 82 proximate outer stepped portion 38. An elongated, flexiblecatheter (not shown for clarity) is coupled to canister 82 proximatefeedthrough assembly 30 to receive optical fiber 44 from assembly 30.Optical fiber 44 is optically coupled to transceiver 88, and may (or maynot) be physically coupled to transceiver 88. Transceiver 88 includes alight source (e.g., a monochromatic light source, such as a lightemitting diode or laser) and a light detector. Transceiver 88 directsoutgoing light signals into the proximal end of fiber 44 and detectsreturning, modulated light signals at the proximal end of fiber 44.Transceiver 88 converts the returning light signals into electricalsignals and provides them to control circuitry 84. Control circuitry 84utilizes the electrical signals received from transceiver 88 todetermine, for example, the current status of a physiological conditionwithin a patient's body.

IMD 80 may optically monitor a wide variety of physiological conditionswithin a patient's body. For example, as shown in FIG. 8, IMD 80 mayserve as an optical interferometer capable of monitoring systolic anddiastolic pressure within an artery 102 (e.g., the femoral or brachialartery). As can be seen in FIG. 8, optical fiber 44 extends throughcanister 82 and into an elongated and flexible catheter 104. Opticalfiber 44 extends axially through the body of catheter 104; however, thedistal tip of fiber 44 terminates a short distance away from the distalend of catheter 104 such that a small gap exists between the distal tipof fiber 44 and the distal end catheter 104. The distal end of catheter104 is covered by a reflective diaphragm 106 (e.g., a silicon or polymermembrane). Diaphragm 106 may flex at its center and thus move closer to,or further away from, the distal tip of optical fiber 44. When thedistal end of catheter 104 is inserted into artery 102 as shown in FIG.8, diaphragm 106 is placed in fluid contact with blood flowing throughartery 102. Consequently, diaphragm 106 will flex (i.e., extendpartially into the distal of catheter 104) in relation to the pressureexerted thereon by the blood flowing through artery 102.

As stated above, transceiver 88 emits light signals into the proximalend of fiber 44. The outgoing light signals propagate through fiber 44to the distal end of catheter 104. When reaching the distal tip of fiber44, the light signals exit fiber 44 and strike diaphragm 106. The lightsignals reflect from diaphragm 106, reenter the distal tip of fiber 44,and return to the proximal end of fiber 44 monitored by transceiver 88.It should thus be appreciated that the length of the optical pathtraveled by the light signals emitted by transceiver 88 corresponds tothe position of diaphragm 106 relative to the distal tip of fiber 44.Due to interference between the reflected light signals and emittedoutgoing light signals, the resulting amplitude of the sensor portion ofthe transceiver will vary depending upon optical path length.Transceiver 88 measures the amplitude of the returning light signals andconverts this measurement into electrical signals that control circuitry84 may utilize to determine the pressure exerted on diaphragm 106 and,therefore, the systolic or diastolic pressure within artery 102.

FIG. 9 is an isometric cross-sectional view of an optical feedthroughassembly 110 in accordance with a second embodiment of the presentinvention. Feedthrough assembly 110 is similar in many respects toassembly 30 described above in conjunction with FIGS. 1, 2, and 4; i.e.,assembly 110 comprises a ferrule 112, an optical fiber 114 passingthrough ferrule 112, and a compression seal stack 116 disposed withinferrule 112 and around fiber 114. Compression seal stack 116 comprises acompression ring 118 and two compression ring seats 120 and 122. Unlikeassembly 30, however, compression ring 118 has a generally tubular shapeand includes an annular depression 124 in a medial portion thereof tofacilitate compression of ring 118. Also unlike assembly 30, compressionring seats 120 and 122 include tapered ends 126 and 128, respectively.Lastly, fiber 114 comprises a relatively short segment having a firstend 130 that terminates proximate compression ring seat 126 and a secondend 132 that terminates proximate compression ring seat 128. As will beappreciated by one skilled in the art, this type of window configurationmay be useful if feedthrough assembly 110 is employed in conjunctionwith, for example, a blood oxygen monitoring system.

Although certain embodiments of the present invention were describedabove as utilizing a window-type fiber (e.g., assembly 110 shown in FIG.9) while others were described as employing an optical fiber extendingsubstantially beyond the ends of the ferrule (e.g., assembly 30 shown inFIGS. 1, 2, 4, and 7), it should be understood that the invention is notlimited to these embodiments and may incorporate optical fibers of awide variety of lengths and types. Furthermore, the term “optical fiber”appearing herein is used in its broadest sense and includes relativelyshort fibers utilized to form optical windows.

In view of the above, it should be appreciated that an opticalfeedthrough assembly has been provided that is suitable for use inconjunction with optical fibers comprising a wide range of materials,including various polymers. It should further be appreciated that theinventive optical feedthrough incorporates a polymeric compression thatmay be manufactured economically and efficiently. Although the inventionhas been described with reference to a specific embodiment in theforegoing specification, it should be appreciated that variousmodifications and changes can be made without departing from the scopeof the invention as set forth in the appended claims. Accordingly, thespecification and figures should be regarded as illustrative rather thanrestrictive, and all such modifications are intended to be includedwithin the scope of the present invention.

1. An implantable medical device (IMD) comprising: an opticalfeedthrough assembly configured to be disposed through a canister of theIMD, the optical feedthrough assembly includes: at least one opticalfiber; a ferrule having first and second open ends and an inner annularsurface; first and second compression seats positioned within saidferrule and each having an aperture therethrough for receiving saidoptical fiber; and a compressible ring positioned within said ferruleand compressed between said first and second compression seats, saidcompressible ring contacting said optical fiber and said inner annularsurface.
 2. An optical feedthrough assembly according to claim 1 whereinsaid first and second compression seats reside within said ferruleproximate said first and second open ends, respectively.
 3. An opticalfeedthrough assembly accord to claim 1 wherein said ferrule includesfirst and second retaining portions for maintaining said first andsecond compression seats in position within said ferrule.
 4. An opticalfeedthrough assembly according to claim 1 wherein said optical fiberincludes a distal end residing proximate said second open end.
 5. Anoptical feedthrough assembly according to claim 11 wherein said opticalfiber further includes a proximal end residing proximate said first openend.
 6. An optical feedthrough assembly according to claim 1 whereinsaid compression ring has a generally tubular shape.
 7. An opticalfeedthrough assembly according to claim 13 wherein said compression ringincludes an annular depression in said inner annular surface.
 8. An IMDcomprising: an optical feedthrough assembly configured to be disposedthrough a canister of the IMD, the optical feedthrough assemblyincludes: at least one optical fiber; a ferrule having first and secondopen ends and an inner annular surface; first and second compressionseats positioned within said ferrule and each having an aperturetherethrough for receiving said optical fiber.
 9. An IMD comprising: anoptical feedthrough assembly configured to be disposed through acanister of the IMD, the optical feedthrough assembly includes: at leastone optical fiber; a ferrule having first and second open ends and aninner annular surface; first and second compression seats positionedwithin said ferrule and each having an aperture therethrough forreceiving said optical fiber; and a compression ring positioned withinsaid ferrule and compressed between said first and second compressionseal seats.
 10. An optical feedthrough assembly according to claim 9wherein said first and second compression seats reside within saidferrule proximate said first and second open ends, respectively.
 11. Anoptical feedthrough assembly accord to claim 9 wherein said ferruleincludes first and second retaining portions for maintaining said firstand second compression seats in position within said ferrule.
 12. Anoptical feedthrough assembly according to claim 9 wherein said opticalfiber further includes a proximal end residing proximate said first openend.
 13. An optical feedthrough assembly according to claim 9 whereinsaid compression ring has a generally tubular shape.